title: Cadaveric study for placement of occipital condyle screws: technique and effects on surrounding anatomic structures.
abstract: OBJECTIVE
  The occipital condyle has never been studied as a viable structure that could permit bone purchase by fixation devices for occipitocervical fusion. The authors propose occipital condyle screw placement as a possible alternative to conventional occipitocervical fixation techniques.
  
  
  METHODS
  Six adult cadaver heads (12 total occipital condyles) were studied, and the StealthStation image-guidance system was used for preoperative planning of occipital condyle screw placement. Morphometric studies of the occipital condyle were performed. A 3.5-mm Vertex screw was then placed in the occipital condyle with image-guided assistance in 3 specimens. Operations in the remaining 3 specimens proceeded using anatomical markers and calculated degrees of angulation for screw placement with a free-hand technique. Postoperatively the cadaver heads were rescanned and reanalyzed to determine the success of screw placement and its effect on hypoglossal canal volume.
  
  
  RESULTS
  All screws were successfully placed with no sign of lateral or medial cortical breach. Two screws had bicortical purchase. There was no change in hypoglossal canal volume in any specimen.
  
  
  CONCLUSIONS
  Occipital condyle screw placement is a safe and viable option for occipitocervical fixation and could be a preferred procedure in selected cases. However, further biomechanical studies are required to compare its reliability to other more established techniques.
authors.affiliation: Department of Neurosurgery, University of Michigan Health System, Ann Arbor, Michigan 48109-5338, USA. flamarca@umich.edu
authors.forename: Frank
authors.initials: F
authors.lastname: La Marca
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Zubay
authors.forename: Thomas
authors.initials: T
authors.lastname: Morrison
authors.forename: Dean
authors.initials: D
authors.lastname: Karahalios
mesh_terms: D000328:Adult; D001269:Atlanto-Occipital Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D001863:Bone Screws; D002102:Cadaver; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007002:Hypoglossal Nerve / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D009777:Occipital Bone / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D011859:Radiography; D013123:Spinal Fusion / Q000379:methods*; D025321:Surgery, Computer-Assisted